The present invention relates to an internal-combustion engine in which each cylinder includes two opposed pistons and it is particularly concerned with an improvement in the air feed system for an engine of the mentioned type.
The effective power per cylinder and the torque of an internal-combustion engine decrease rapidly when the engine operates at high speed. It is known that this results from a bad cylinder charging with air-fuel mixture, which substantially diminishes the effective average pressure applied to each piston. A standard passenger-car has a cylinder charging ratio which does not exceed about 80% at an engine speed of about 4000 t/m.
In a two-stroke-cycle engine the scavenging and the cylinder charging ratio are worse at high engine speeds than in a standard four-stroke-cycle engine as a consequence of the strokes succeeding faster. This is the reason why a standard two-stroke-cycle engine is generally badly suitable for operation at high speed. However, the two-stroke-cycle engine exhibits advantages which make it an attractive engine to be used in many appliances and recently even in airplanes.
The problem to be solved, however, still remains to improve the volumetric efficiency of the two-stroke-cycle engine, that is to achieve a good scavenging of the combustion chamber such that the cylinder charging ratio is substantially improved.